Examples of a method of pixel addition in a complementary metal oxide semiconductor (CMOS) image sensor include a comparator capacitance addition method and a counter addition method.
The comparator capacitance addition method is a method by which a plurality of capacitances is provided in parallel on an input side of a comparator of a column ADC, and signals from a plurality of vertical signal lines are added in the capacitances. The counter method is a method by which digital addition is performed in a counter circuit within the column A/D converter (ADC).
The comparator capacitance addition method is described, for example, in Patent Document 1. An image sensor described in Patent Document 1 is configured such that two vertical signal lines are provided in each column, and weighted addition of outputs of two pixels is performed in the input capacitances of the comparator.
In addition, the counter addition method is described, for example, in Patent Document 2. An image sensor described in Patent Document 2 is configured to perform digital addition by performing A/D conversion on each output of two pixels with resolution or gain changed.